Bacillus thuringiensis (B.t) produces an insect toxin designated as .delta.-endotoxin. It is synthesized by the B.t. sporulating cell. The toxin, upon being ingested in its crystalline form by susceptible insect larvae, is transformed into biologically active moieties by the insect gut juice proteases. The primary target is insect cells of the gut epithelium, which are rapidly destroyed.
The reported activity spectrum of B.t. covers insect species within the order Lepidoptera, many of which are major pests in agriculture and forestry. The activity spectrum also includes the insect order Diptera, which includes mosquitos and black flies. See Couch, T. L. (1980) "Mosquito Pathogenicity of Bacillus thuringiensis var. israelensis," Developments in Industrial Microbiology 22:61-76; Beegle, C. C., (1978) "Use of Entomogenous Bacteria in Agroecosystems," Developments in Industrial Microbiology 20:97-104. U.S. Pat. No. 4,910,016 discloses a B.t. strain active against coleopteran and lepidopteran pests. U.S. Pat. No. 4,849,217 discloses B.t. strain MT 104 as active against the Egyptian alfalfa weevil.
The lesser mealworm (Alphitobius diaperinus) is a cosmopolitan pest of households, stored grain facilities, and poultry houses. It usually feeds on damp and moldy grain, milled products, and spoiled foods. Due to significant growth in the poultry industry in recent years, this insect has become one of the major pest species present in the litter and structural components of poultry houses. The larvae of A. diaperinus ingest chicken feed and other organic matter (including dead or moribund chicks), are reservoirs for a multitude of pathogens which are threats to poultry production, and cause extensive structural damage to poultry houses by tunneling into the insulation and soft wood of the facility. The loss of insulation due to the holes and tunnels bored by A. diaperinus larvae results in greater heating costs as well as poorer feed conversion efficiency by poultry due to the lack of adequate temperature control in the poultry houses. Additionally, since poultry will feed on these insects as an alternative food source, they may experience lesser weight gains than if fed their normal nutrient balanced diet. The larvae of A. diaperinus have also been implicated in causing lesions on poultry and may increase their susceptibility to disease due to dust stirred up by the birds while they are scratching for insects. A. diaperinus may also cause allergic reactions in humans.
Current control techniques are inadequate for controlling this pest and will not eradicate the pest problem. They include the following: 1) thoroughly cleaning the poultry house and having it remain empty for a prolonged period of time; 2) applying insecticides to the structure and floors of the house after it is cleaned; 3) using insect growth regulators; and 4) using steinernematid and heterorhabditid nematodes as beetle entomopathogens. These methods are ineffective and expensive. Thus, there is an urgent need for the effective control of the lesser mealworm.